In the past eight years a large number of designs for knee joint replacement prostheses have been developed. Many of these have been used with varying degrees of success. The testing of these designs in the laboratory was originally haphazard because of the lack of an experimental animal with knee joint characteristics similar to man. More recently the preclinical testing has improved to the point where it is now readily accepted that important data can be obtained prior to actual clinical use. This research program has been underway for five years and has contributed to the development of knee simulators and other testing devices and techniques used to evaluate endoprostheses. Using these methods, the newest prostheses will be subjected to rigorous testing with suggested modifications or modes of failure identified as precisely as possible. This will be followed by clinical studies involving pre-and postoperative evaluation of patients undergoing knee replacement surgery. The correlation of laboratory and clinical findings for each prosthesis is an important facet of the project. For this purpose, the Principal Investigators will collaborate with other centers in order to obtain maximum data on the widest variety of prostheses available. Through this mechanism it is hoped that the optimum prosthetic design or designs can be generated.